(1) Field of Invention
This invention is related to structures and buildings classification. The invention is devices that are placed within the structures frame, such as buildings and bridges, to increase their overall damping, to improve their performance by dissipating part of the energy transferred to them from Earthquakes, Wind and/or similar hazards.
(2) Description of the Related Art
It is known that increasing the damping in a structure will result in improvement in the response and performance of the structure under earthquake vibration, wind forces or any hazard of similar nature. All structures have damping, which causes them to stop vibrating. This damping is the result of internal factors such as the damping of the material of the structure, the movement in the connections or external factors such as the air resistance. The typical damping in a structure can approximately vary between 2 to 7% in the fundamental mode of vibration. With the supplemental dampers, the damping can be increased substantially to a desirable value of 15 to 25% or more in the fundamental mode of vibration. Those increases in the damping improve the performance of the structures, such as reduction in the side sway, reduction in the base shear and ultimately the reduction in the stress in the structural members and connections. At the same time the structures are build the same traditional way with the structures being supported by a regular foundations system.
This invention is made of Rubber or Rubber like material that is attached or bonded to Steel or steel like material and is placed on the top of the structure's bracing or shear walls. It can be also placed in the intersection of the bracing members or as part of the bracing members themselves. It is non-gravity load carrying device. However, it can be designed to be load bearing when it is placed for example on the top of shear walls.
Currently, there are several types of passive supplemental dampers; none of them use Rubber as the energy dissipating material. Those dampers are Friction dampers, Viscoelastic dampers, yielding metal dampers, Fluid viscous dampers. The friction dampers dissipate energy as a result of the friction between two metal surfaces, and have the disadvantage of deterioration when the friction surfaces deteriorate with the repeated use and time. Viscoelastic damper performance deteriorates with the changes in temperature and large strains. Yielding metal dampers dissipate energy due to the nonlinear deformation in the metal after yielding, it has the disadvantage of having residual strain in the metal due to the yielding, which make it less efficient or it might fail due to the repeated yielding and residual strains. Fluid viscous dampers have the disadvantage of being too expensive and the fluids might leak during the long life of the structures.
Another technology, which uses Rubber, is Base Isolators, which are placed between the structure and its foundations to separate the structure from the earthquake vibration. Isolators are also placed in other places in the structure to isolate sensitive equipment from their bases. The Base Isolators carry the weight of the structure and that is very serious drawback, which limits its use to smaller structures only. It requires back up system to carry the structure if the Base Isolator fails. The Base Isolators require periodic testing and maintenance. This is a serious disadvantage because of the long life of the structures. Frequently, many structures change owners and/or use. In many cases the structure's drawings are lost and the designer or the contractor could not be located, which poses a serious risk because of the needed inspection and maintenance. The Base Isolators cause large movement between the foundation and the structure under earthquakes vibration and wind forces, this is a big disadvantage because it requires many components of the structure to be designed to accommodate that movements. All of those disadvantages have limited the use of Base Isolators. It is most frequently used for retrofitting and upgrading of existing structures.
The Isolators technology is completely different from the supplemental damper technology. The Isolators as the name indicate serves to isolate the structure or the sensitive equipment from the vibration. The supplemental dampers on the other hand, as the name implies serves to supplement and increase the damping in the structure and at same time it doesn't cause the undesirable relative movement as in the case in the Isolators.